When vehicle air bags were initially introduced on the market, it was necessary to remove driver control functions from the steering wheel and install them on stalks that emanated from the steering column. Typically, the only two items which remained wheel-mounted were the air bags and the horn. The signal for the horn was transferred from the wheel to the column through slip rings. The slip rings consisted of a ball contact located on the steering wheel and a circular conductor which was part of a "clock spring". The clock spring was a molded plastic part which housed a two conductor ribbon cable that connected the air bag to its control module. Such a clock spring is capable of maintaining electrical connections during rotation of the wheel.
The numerous design concepts comprising adaptations of slip rings and clock rings have been fraught with problems and are of limited economic and practical value. Slip ring arrangements have always suffered from reliability and performance problems due to the inherent nature of the slip ring structure itself. The electrical integrity of the contacting methods necessarily depreciate over time and from dirt and/or wear and varying ambient conditions. In addition, as the demand for the placement of driver controls back onto the steering wheel has become greater, the complexity and cost to manufacture clock springs have increased, and their reliability have decreased. Attempting to compensate for the increased cost and decreased reliability of clock springs, some applications have included the use of a rotary transformer between the steering wheel and the steering column to generate a "contactless" system. But the known approaches for firing the gas generators (squibs) that deploy the air bags all use a direct firing method which necessitates a complex and expensive rotary transformer. Moreover, the known methods for transferring data between steering wheel and the column require a transformer with very limited in-line and runout assembly tolerances.
Accordingly, it is desirable to have an improved apparatus and method for firing air bag squibs and for transferring power and data between the vehicle steering wheel and the steering column.